1. Technical Field
Embodiments of the subject matter described herein relate generally to systems that power inverter-driven loads. Other embodiments relate to systems for powering a vehicle.
2. Discussion of Art
One or more alternators may be joined with an engine of a powered vehicle to generate electric current. The current may be supplied to traction motors that provide the motive force that propels the vehicle, and to non-propulsion electric loads that do not propel the vehicle but provide other functions. Examples of non-propulsion electric loads include heating, ventilation, radial fans, air cooling (HVAC) subsystems, lights, electric circuits for personal use, and the like.
The non-propulsion electric loads may be powered by a head end power (HEP) system. Some HEP systems provide power to non-propulsion loads that operate on a fixed voltage and fixed frequency electric current. For example, some known non-propulsion loads that draw power from HEP systems run off of three phase alternating current having a voltage of 480 volts and a frequency of 60 Hz. The HEP systems may receive electric current for the non-propulsion electric loads from the tractive circuit in a transformed manner. For example, a transformer may inductively couple the tractive circuit with an auxiliary circuit that supplies the current to the non-propulsion electric loads. In addition to or as an alternative to the transformer, one or more boost choppers may be provided to increase the voltage on the tractive circuit to a larger voltage on the auxiliary circuit. One or more filters between the tractive and auxiliary circuits may be necessary to remove unwanted frequencies of the current before supplying the current to the non-propulsion loads.
The boost choppers and/or transformers increase or decrease the voltage supplied to the auxiliary circuit from the tractive circuit. The engines of some vehicles operate above a determined speed to ensure that sufficient torque is supplied to the alternator, and therefore sufficient voltage is supplied from the alternator to both the tractive circuit and the auxiliary circuit. For example, during motoring of the vehicle, the engine may operate above a first determined speed to ensure that sufficient voltage is generated and supplied to the tractive motors, and when the vehicle is idling the engine may still need to operate above a second determined speed to ensure that sufficient voltage is generated and supplied to the non-propulsion loads of the auxiliary circuit.
Some vehicles include two or more separate engines that power the tractive and auxiliary circuits. One engine causes an alternator to generate current for the tractive circuit, while another engine causes another alternator to create current for the auxiliary circuit.
It may be desirable to have a system that differs in function from those systems that are currently available.